python_context.py

# _*_ coding: utf-8 _*_

"""
python_context.py by xianhu
"""

import contextlib


# 自定义打开文件操作
class MyOpen(object):

    def __init__(self, file_name):
        """初始化方法"""
        self.file_name = file_name
        self.file_handler = None
        return

    def __enter__(self):
        """enter方法，返回file_handler"""
        print("enter:", self.file_name)
        self.file_handler = open(self.file_name, "r")
        return self.file_handler

    def __exit__(self, exc_type, exc_val, exc_tb):
        """exit方法，关闭文件并返回True"""
        print("exit:", exc_type, exc_val, exc_tb)
        if self.file_handler:
            self.file_handler.close()
        return True

# 使用实例
with MyOpen("python_base.py") as file_in:
    for line in file_in:
        print(line)
        raise ZeroDivisionError
# 代码块中主动引发一个除零异常，但整个程序不会引发异常


# 内置库contextlib的使用
@contextlib.contextmanager
def open_func(file_name):
    # __enter__方法
    print("open file:", file_name, "in __enter__")
    file_handler = open(file_name, "r")

    yield file_handler

    # __exit__方法
    print("close file:", file_name, "in __exit__")
    file_handler.close()
    return

# 使用实例
with open_func("python_base.py") as file_in:
    for line in file_in:
        print(line)
        break


# 内置库contextlib的使用
class MyOpen2(object):

    def __init__(self, file_name):
        """初始化方法"""
        self.file_handler = open(file_name, "r")
        return

    def close(self):
        """关闭文件，会被自动调用"""
        print("call close in MyOpen2")
        if self.file_handler:
            self.file_handler.close()
        return

# 使用实例
with contextlib.closing(MyOpen2("python_base.py")) as file_in:
    pass